1. Field of the Invention
This invention relates generally to the production of non-traditional fuels, often referred to as synthetic fuels. More particularly, this invention relates to the creation of such fuels using existing stockpiles of coal fines, coal dust, and other similar small particles of virgin coal. More particularly yet, this invention relates to using emulsions of tall oil and tall oil pitch, a by-product of the paper industry, in the creation of such fuels.
2. Description of the Prior Art
For centuries coal has been mined as a source of fuel. During these years, numerous improvements have been made to increase mining efficiency and safety, and to improve the overall quality and purity of the end product. However, one drawback of coal mining is the by-product of coal fines that frequently end up abandoned into waste pits scattered throughout the countryside. These coal fines constitute up to 20% of the coal being mined, and are found in the waste stream generated by the initial washing and filtering of the coal from the mine. Although coal fines include particles as small as dust motes, the term can also include pieces of coal up to about one-half inch in diameter. This material has traditionally been abandoned to waste, deposited in the form of “coal tips,” because it has been economically inefficient to handle such sizes as they are brought to the point of being burned for their energy content. As a result, literally millions of tons of such material has been produced over the years, and currently lays dormant at or near mining sites. Not only does this non-use pose a great waste of valuable natural fuel resources, but it also poses a threat to the surrounding environment. In addition to respiratory hazards presented by the dust-sized particles, the large surface area associated with stockpiles of such particles poses a high risk for spontaneous combustion such as the type known as a dust explosion.
These environmental issues, together with the growing concern of the limited existing amount of natural fuel resources, has led to an increased interest in utilizing these dormant coal fines, as well as developing an alternative use of virgin coal.
Attempts to utilize coals fines as fuel include the method disclosed in White (U.S. Pat. No. 5,916,826; issued 1999), which teaches a method of pelletizing and briquetting coal fines using bio-binders produced by liquefaction of biomass. Unfortunately, this process is extremely costly, primarily because of the required liquefaction process, which is carried out in an oxygen-free environment at elevated temperatures, e.g. between 450 degrees and 700 degrees F., and elevated pressures, typically between 200 psi and 3,000 psi. The resulting liquid is then sprayed on coal fines that have themselves been heated to at least 250 degrees F., after which the coal and the liquid are allowed to react at about 300–400 degrees F. Although this method serves to alleviate certain environmental concerns, the high costs of reclaiming coal using this process undercuts the basic usefulness of the invention itself.
Another recent example of the attempt to use coal fines as fuel, Ford (U.S. Pat. No. 5,453,103; issued 1995), discloses a method of forming solid fuel pieces from coal fines by combining and mixing water, hydrochloric acid, a conditioner, and a polyvinyl acetate (PVA) emulsion and then compressing the resulting slurry into solid fuel pieces. Although this process is effective, its requirement of PVA, which must be separately created for this particular use, makes the Ford process economically and environmentally inefficient in comparison with a process founded entirely on the use of constituents that are already present, and which some of the constituents are not being devoted to any economical purpose. In other words, a process that consumed both coal fine waste and another hitherto waste element would be more desirable than the Ford process.
A process that does use as input primarily waste products from other industrial operations is revealed by Major (U.S. Pat. No. 6,013,116; issued 2000), which teaches a composition for binding coal fines into larger pieces, typically called briquets. The briquet-binder composition of Major can be produced using an asphalt base, sodium carbonate pulping liquor, and a surfactant. However, for optimal binding results, strength-increasing additives such as latex, vinyl derivatives, cellulose, cellulose derivatives, peat moss, starch, starch derivatives, and various pulps need to be added to the binder composition. (The addition of lignosulfate, cement, rubber, and plastics is also taught by Major.) Although this process does use various waste products of other industries in transforming coal fines into a more usable fuel source, the complexity of the binding material makes the process quite complex, thereby reducing the economic viability of the overall method.
An older process of reclaiming coal fines is disclosed in Dondelewski (U.S. Pat. No. 4,357,145; issued 1982). In Dondelewski, coal fines are combined with a liquid by-product of the pulp and paper industry, namely a liquid containing tall oil, tall oil pitch, or mixtures thereof (“tall oil mix”). Tall oil and tall oil pitch are by-products from the digestion of wood by the Kraft (sulfate) paper manufacturing process. In the Dondelewski method, the coal fines are first put into the form of a slurry by mixing them with water. After the slurry has been formed, it is fed to a conditioning tank where it is mixed with tall oil mix. In the conditioning tank, the tall oil mix adheres to and thus coats the surfaces of the individual coal particles, after which the slurry of now-coated coal particles and excess tall oil mix is introduced into a flotation cell, where the coated coal particles are separated from the excess tall oil mix and most of the water. Vacuum filters, vibratory screens and centrifuges may be used to remove excess liquid, a necessary step since most coal-consuming furnaces cannot tolerate a high moisture content. Again, the process of Dondelewski has as its feed stock predominantly industrial by-products, it is very process intensive, first requiring large vats to mix the coal slurry and tall oil mix, then further processing to remove excess water and tall oil mix followed by drying the end product. Thus, the method of Dondelewski does not satisfy the condition of using industrial by-products to produce a synthetic fuel that is economically competitive with the fuels that the synthetic fuel is intended to supplant, or which in general is in competition with it as a fuel source.
Therefore, what is needed is an economical and environmentally friendly method of using industrial by-products traditionally discarded as waste as the feed stock for a new fuel. What is more specifically needed, in view of the millions of tons of coal fines deposited throughout the landscape, is such a method that uses coals fines as all or part of the feed stock. Finally, what is needed is such a process that by whatever means results in a fuel that is economically viable in the marketplace, so that industries now holding hegemony over the referenced industrial by-products, and in particular the coal fines, will be induced to use up those by-products, removing them from the category of stored and hazardous waste.